It bugs me when I come across multiple charts that seem to contradict each other. I realize that different assumptions for safety factors can impact the choice of wire for a given application, but I'd still expect the choices to be within a gauge or so. I've used the TESSCO chart for years as it seemed to have relatively similar ratings to other charts I'd compared it to. Just goes to show that just because you found it on the Internet, ... 
Another Battery Question
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It bugs me when I come across multiple charts that seem to contradict each other. I realize that different assumptions for safety factors can impact the choice of wire for a given application, but I'd still expect the choices to be within a gauge or so. I've used the TESSCO chart for years as it seemed to have relatively similar ratings to other charts I'd compared it to. Just goes to show that just because you found it on the Internet, ...
There are many things that can have an impact on how much current a wire can carry that might impact any given chart. Single wires in open air can carry much more current than multiple wires of the same size running in a conduit the ability to dissipate heat is an important factor. wires run in a tight space will retain heat and should be sized larger than a single wire out in the open air. Speaking as a person who many moons ago was an industrial electrician I would choose to oversize wires I used in the hot confines of the Slingshots engine compartment or other areas where ventilation is restricted.
As a side note I have always been amazed at how much smaller the wires are that run between above ground power poles are when compared to the wires they use when bringing that same power off the pole to run underground.
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For the uninformed. Here is a picture of wires with no electricity running through it:
Here is a pic of the same wires full of electricity:
Always happy to contribute!
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As a side note I have always been amazed at how much smaller the wires are that run between above ground power poles are when compared to the wires they use when bringing that same power off the pole to run underground.
Power = Current times Voltage. The transmission system carries high voltage long distances by using extremely high voltage - therefore, the current being carried is much lower - therefore, wire diameter can be smaller. In underground transmission, AC current is very limited for distance due to inherent high capacitance in that application. When you see a line coming down from a pole, the voltage has been stepped down by a transformer and/or it’s not underground for an excessively long distance & the diameter will indeed have to be larger - just a basic fact.
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Power = Current times Voltage. The transmission system carries high voltage long distances by using extremely high voltage - therefore, the current being carried is much lower - therefore, wire diameter can be smaller. In underground transmission, AC current is very limited for distance due to inherent high capacitance in that application. When you see a line coming down from a pole, the voltage has been stepped down by a transformer and/or it’s not underground for an excessively long distance & the diameter will indeed have to be larger - just a basic fact.
What you say is correct and I am very familiar with both Ohms law and Watt's law, Here in the valley we have very large metal poles that are at the end of the high voltage lines coming into town. The wires at the end are changed to much larger wires (no transformer involved) these larger wires then go inside the pole and continue underground to the power distribution locations. You should see them, the difference in the wire size is very substantial.
As you note current is the primary factor in determining wire size, but other factors are also important and one of those is the ability to dissipate heat. wires in a confined space like a conduit will not dissipate heat as easily and must be larger another factor that we had to consider when I was an electrician was the number of wires in a conduit you cant just force as many wires as can fit even if the wire were the correct size it would over heat if there were too many in the pipe because of the inability to dissipate the heat caused by so many wires and the lack of air space.
My experience with electricity and electronics is limited to what I learned as an electrician and what I learned building Ham radios a million years ago, I have almost zero experience with automotive wiring, but like I said, if the charts called for a #4 wire in my Slingshot I would most likely run #2 and if it called for #12 for a 20 AMP circuit I would use #10
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What you say is correct and I am very familiar with both Ohms law and Watt's law...
... if the charts called for a #4 wire in my Slingshot I would most likely run #2 and if it called for #12 for a 20 AMP circuit I would use #10That's always the safest thing to do. As it states at the bottom of the TESSCO chart I linked earlier - "For safety and best resultsWhen (sic) circuit is longer than 10 feet, always use the next larger gauge size".
